2004-2007 Subaru Impreza Front vs Rear Brakes: What Wears First and What to Replace

By Core Brake Parts Tech Team — Circleville, OH warehouse

On a 2004-2007 Subaru Impreza the front brakes almost always wear out first. Every trim of this generation uses four-wheel disc brakes with ABS, and because the car's weight pitches forward when you stop, the front pads and rotors do most of the work. The rears last longer, but they are not maintenance-free: the rear calipers and the parking brake shoes inside the rear rotors have their own failure habits, and salt-belt cars need a hard look at the steel brake lines.

How the brakes are laid out on the 2004-2007 Impreza

This is the GD/GG-generation Impreza: the 2.5 RS, 2.5i and Outback Sport, plus the WRX and the WRX STI. Published specifications for the 2004 Impreza 2.5 RS list four-wheel disc brakes with anti-lock brakes as standard, on a car that weighs about 1,350 kg (roughly 2,976 lb). So there are no rear drums to worry about on the regular Impreza of these years; you are dealing with pads and rotors at all four corners.

The owner's manual for the 2006 Impreza has separate sections for the disc brake pad wear warning indicators, the ABS warning light and an Electronic Brake Force Distribution (EBD) system. EBD uses the ABS hardware to adjust how much pressure goes to the rear brakes depending on load. That matters for this topic: the rear brakes on these cars are asked to do a real share of the stopping, which is why rear pads on an Impreza are not the "set it and forget it" part they are on some older front-heavy sedans.

The performance trims are a different animal. An Impreza brake reference guide lists the 2003-2007 STI with a 325 mm vented front disc and Brembo four-piston calipers, and a 316 mm vented rear disc with Brembo two-piston calipers. The WRX uses its own larger vented setup that is not interchangeable with the 2.5 cars. The same guide notes that in late 2004 Subaru switched the STI from a 5 x 100 to a 5 x 114.3 stud pattern (the "widetrack" change), so an STI rotor for one side of that change will not bolt onto the other. Always confirm the trim, and on an STI the build date, before ordering rotors.

Symptoms: how to tell which end needs work

Front brake wear shows up as a high-pitched squeal while driving that goes quiet when you press the pedal (the wear indicator tab touching the rotor), a pulsation in the pedal or steering wheel when stopping from highway speed, or a grinding noise once the pad material is gone. Grinding means metal on metal, and the rotors will need replacing, not just resurfacing.

Rear brake problems are sneakier because you feel less of them through the pedal. Look for:

• A squeal or scrape from the back of the car, especially in reverse.
• One rear wheel noticeably hotter than the other after a drive, or a burning smell. That points to a caliper slide pin or piston that is sticking.
• Uneven pad wear on one caliper: the inner pad worn to the backing plate while the outer pad still looks thick is the classic sign of a seized slide pin.
• A parking brake lever that has to be pulled much higher than it used to, or that no longer holds the car on a hill. The parking brake shoes live inside the rear rotor hat and wear independently of the rear pads.

The quickest check is visual. Pull the wheels and look at the pads through the caliper window, and measure the rotors against the minimum thickness stamped on the rotor or listed in the factory service manual. Also check the brake fluid reservoir under the hood: as pads wear, the caliper pistons move out and the fluid level drops toward MIN, so a low reservoir with no leak is often just worn pads.

Why the fronts wear first, and what makes the rears wear early

Under braking, weight transfers onto the front tires, so the front axle can use more braking force before the tires lock. Brake systems on passenger cars are designed around that, which is why the front pads and rotors are larger and wear faster on nearly every car, the Impreza included. A common pattern is replacing front pads more often than rears, but your mileage depends heavily on how and where you drive.

Rear pads wearing out as fast as or faster than the fronts is not normal, and it usually has a mechanical cause:

• Sticking slide pins on the rear caliper, from dried-out grease or a torn pin boot letting in water and road salt.
• A dragging parking brake that is adjusted too tight or has a rusted cable, which holds the shoes against the drum-in-hat and heats the rotor.
• A seized caliper piston, more common on older cars that have never had a brake fluid flush.
• Mismatched pads, such as an aggressive front pad paired with a worn-out original rear, which changes how the car shares the braking work.

Check the brake lines on salt-belt cars

Subaru ran a safety recall (NHTSA campaign 14V-311, Subaru code WQK-47) for brake line corrosion caused by salt water splashing through a gap in the fuel tank protector. That recall covered 2008-2011 Impreza and 2008-2014 WRX and STI models, plus other Subarus, registered in salt-belt states. The 2004-2007 Impreza is not on that list, but these cars are older still, and many have spent twenty winters on salted roads.

The recall bulletin explains that the center and rear brake lines work independently, so if one line perforates the car can still stop on the other system, with the brake warning light on and a longer pedal. On a 2004-2007 Impreza from Ohio, Michigan, Pennsylvania, New York or any snowy state, inspect the hard lines along the underbody and over the rear of the car every time it is on a lift for brakes. Rusted or flaking lines should be replaced with new brake lines, and cracked or swollen rubber hoses at each wheel with new brake hoses.

The fix: what to replace, and what to replace with it

Front brake job. Replace pads and rotors as a pair on the same axle, left and right together. On a car this age, new rotors usually make more sense than machining the old ones, because many original rotors are already close to minimum thickness. Browse brake pads and brake rotors by vehicle, and choose ceramic brake pads if you want low dust and quiet daily driving.

Rear brake job. Do the same pads-and-rotors pair, and while the rotors are off, inspect the parking brake shoes and hardware inside the hat. If the shoe lining is thin or the springs are rusted, replace them now; you will not want to take the rotors off twice. Clean and re-grease the caliper slide pins with a brake-specific lubricant, and replace any pin boot that is torn.

At the same time:

• New clips, shims and pins from a brake hardware kit. The old anti-rattle clips lose their spring after years of heat.
• A caliper that is leaking, has a torn piston boot or will not retract should be swapped for a replacement from our brake calipers range rather than forced back into service.
• A brake fluid flush with the fluid type printed on the reservoir cap. Brake fluid absorbs moisture from the air, and Subaru's Impreza manual warns against mixing DOT 3 and DOT 4 fluids or different brands.

Tighten caliper bracket bolts and lug nuts to the values in the factory service manual, and bed in new pads with a series of moderate stops before any hard braking.

How hard is the job?

A front pad and rotor job on the 2.5 RS, 2.5i or Outback Sport is a good first brake job for a home mechanic with a jack, stands and basic hand tools. The rotors come off once the caliper bracket is removed, and a rusted rotor can take some persuasion to free from the hub.

The rear is a step harder because of the parking brake. The shoes can hold the rotor on, so you may need to back off the parking brake adjuster before the rotor will come free, then readjust it afterward. If you are replacing the shoes too, plan for extra time and take a photo of the spring layout before you take anything apart. STI owners with the Brembo calipers have a simpler pad swap, but the rotors are large and costly, so it pays to be sure of the exact fitment first.

Frequently Asked Questions

Does the 2004-2007 Subaru Impreza have rear drum brakes?

No. Published specifications for this generation list four-wheel disc brakes with ABS. The only drum-style part at the rear is the small parking brake shoe set inside each rear rotor hat.

Should I replace front and rear brakes at the same time on my Impreza?

Only if both ends are worn. Fronts usually wear first, so it is normal to do fronts alone. Always replace both sides of the same axle together, and inspect the rears whenever you do the fronts.

Why are my Impreza's rear pads worn more than the fronts?

That usually points to a sticking rear caliper slide pin, a dragging parking brake, or a seized piston. Fix the cause when you replace the pads or the new ones will wear out just as fast.

Do WRX and STI brake parts fit a regular Impreza 2.5?

No. The WRX and STI use larger, different brake systems, and the STI also changed stud pattern in late 2004. Order parts by exact trim and model year.

Is my 2004-2007 Impreza covered by the Subaru brake line recall?

The brake line corrosion recall 14V-311 begins with the 2008 Impreza, so these years are not included. Salt-belt cars of this age should still have their brake lines inspected at every brake service.

Sources

1. Auto123 - 2004 Subaru Impreza 2.5 RS technical specifications - four-wheel disc brakes, standard ABS, 1,350 kg curb weight
2. Scoobyparts - Impreza brake disc size and pad shape guide - 2003-2007 STI Brembo rotor sizes and caliper types, late-2004 stud pattern change
3. NHTSA / Subaru of America - Recall 14V-311 (WQK-47) dealer announcement - brake line corrosion recall, covered model years, independent center and rear brake lines
4. Subaru 2006 Impreza owner's manual - pad wear warning indicators, ABS and EBD system sections
5. Subaru Impreza owner's manual - recommended brake fluid - do not mix DOT 3 and DOT 4 fluids or brands